Maize rough endosperm6 is a predicted RNA helicase required for miRNA processing and endosperm cell patterning

Abstract

Maize rough endosperm mutants have defective kernels with a rough, etched, or pitted endosperm surface. Molecular genetic analysis of this mutant class has identified multiple RNA processing proteins critical to endosperm development. Here, we report that rough endosperm6 (rgh6) encodes a predicted DEAD-box RNA helicase required for miRNA processing. Mutant rgh6 kernels reduce grain fill and increase relative transcript levels of markers specific to epidermal endosperm cell types. B-A translocation crosses revealed that rgh6 mutant endosperm inhibits normal embryo development. We mapped the rgh6 locus to a three gene interval and confirmed it encodes a predicted DEAD-box RNA helicase with two independent transposon-tagged alleles. Transient expression of a RGH6-green fluorescent protein (GFP) fusion is localized to nucleolus and nuclear speckles consistent with a function in nuclear RNA processing. Mutant rgh6 endosperms have increased precursor miRNA and decreased mature miRNA levels indicating that rgh6 impacts miRNA processing. Our study demonstrates that precursor miRNA processing and miRNA target regulation are required for normal endosperm development.